Jesus can be King, and Mighty God, over the whole world. But in the context of Revelation 16, He's one of the Kings from the East.
It says kings FROM the east, not OF the east.
"The sixth angel poured out his bowl on the great river Euphrates, and its water was dried up, to prepare the way for the kings from the east.
Due to the earth's rotation, when visitors come from heaven, they appear to be coming from the east. Remember Jesus saying like lightning shinning from the east and to the west?
"For just as the lightning comes from the east and flashes as far as the west, so will be the coming of the Son of Man.
And the angel ascending from the east with the seal of God?
"And I saw another angel ascending from the east, with the seal of the living God.
And the news from the east alarming the stern faced king in Daniel 11?
The drying up of the Euphrates is also symbolic language for destruction coming from the north.
Destruction always comes from the north.
King of the north, the Assyrian, is symbolic language for King of destruction, the son of perdition.
It's the same concept as the drying up of the great river Euphrates.
The Euphrates river was a large natural obstacle preventing invading armies from the north coming down into Israel and bringing destruction. When this river dries up, the green light is given for the Kings FROM the East to bring Divine Destruction.
Like the angel ascending from the East bringing the seal of God, and the lightning of Jesus coming from the east to the west, the Kings from the East are heavenly Visitors. God the Father, and Jesus:
"They called to the mountains and the rocks, “Fall on us and hide us from the face of him who sits on the throne and from the wrath of the Lamb!
( I wouldn't be waiting for Hal Lindsey's Asian army to be marching through the Euphrates Riverbed. LOL)
But Divine Destroyers came from the north.
Nebuchadnezzar came down from the north and wiped out Jerusalem.
"For I am bringing disaster from the north, even terrible destruction." ... Set up the banner in Zion: come together, do not delay: for I bring evil from the north wind, .
"Then the LORD said, "This means destruction will break out from the north on all ... cry, O city; Melt away, O Philistia, all of you; For smoke comes from the north, .
"Egypt is like a very fair heifer, but destruction cometh; it cometh out of the north.
"Then the LORD said to me, "Out of the north the evil will break forth on all the inhabitants of the land.
And notice during a time of restoration God removes the northerner:
“I will remove the northerner far from you, and drive him into a parched and desolate land, his vanguard into the eastern sea,
Peaceful Sabbath.